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A Self-Defined Variable Time Slot Protocol of LoRa Sensor Network for Elderly Care
Hua Liang, Guangxiang Yang, Guangling Yu, Delin Zhang, Baofeng Yang and Xiaoheng Wang

LoRa technology has gained much attention due to its features in wireless sensor networks (WSNs) applications. However, LoRaWAN still has challenges to be addressed, such as unfair energy consumption and robustness. To characterize and optimize the network application performance, the authors have introduced a self-defined variable time slot data transmission mechanism (SDVTS), in which the data transmission cycle can be adaptively changed or freely defined for higher efficiency. Each end-device is clock synchronized. The data packet collision is much less with LoRaWAN by multi end-device clock synchronizing. Furthermore, the data transmission delay is reduced through an uplink and downlink data frame format re-design. The SDVTS scheme is able to achieve a compromise between energy consumption and transmission efficiency by adaptively changing the data transmission cycle in terms of the actual application requirement. The experiment results show that the energy consumption of the SDVTS node can be greatly reduced compared to the LoRaWAN node in the condition of fewer nodes, shorter time slots or longer data transmission periods T. The energy consumption is influenced by the data transmission period T, time slot Tsi and the number of nodes N. For example, the energy consumption of SDVTS decreases significantly with the increasing data transmission period when the number of nodes remains constant. We can find a compromise between energy consumption and other network parameters according to the statistical SDVTS model proposed in this paper.

Keywords: wireless sensor networks, Self-defined variable time slot (SDVTS), elderly care, LoRaWAN, energy consumption